Do you use firefox? You're sure that it is the forum software checking the spelling? I thought that my browser (firefox) was doing the checking. If you highlight a word and rightclick on it it gives some suggestions on that word. Also the possibility to add the word to the dictionary or to disable spell checking.

I am 100% certain that it's Firefox that does this. I am Dutch and all my english text is undercurled (yeah... hence the spelling errors ;-) ). Maar type ik dit in het Nederlands dan is er niets onder"streept" (But if I type this in Dutch then nothing is under"lined").